Yard tractors typically comprise a four-point mounting system for mounting the cab to the frame of the semi-tractor. In some semi-tractors, the cab includes a deck portion whereby the cab is connected directly to the deck portion with the cab mounted to the frame. Others have the deck portion mounted to the frame with the cab riding on top of and connected to the deck portion.
A yard tractor is a semi-tractor having a short wheel base and may have distinct structural features, such as an elevating fifth wheel, for performing various specialized tasks. Typically, a yard tractor has a one-man cab configured to cover only about one-half of the tractor and is positioned either on the right hand or left hand side of the tractor, depending on the location of the tractor's country of manufacture, location of intended use and/or the user's preference. Some countries require the operator to be positioned on the right hand side while others require positioning on the left hand side. Either configuration causes a shift of the center of gravity to one side or the other of the tractor centerline depending on which side the cab is positioned. This shift in the center of gravity creates unique characteristics in the response of the cab to shocks and vibrations.
Normally, the cab of a yard tractor is separated from and placed atop of the deck, with the deck covering the entire front axle area and engine. In addition, the rear axle of a yard tractor usually has no axle-to-frame suspension due mainly to desired performance characteristics or criteria. Without some type of suspension or isolation system, shocks and vibrations generated by movement of the yard tractor over rough roads or terrain are transmitted through the frame to the cab. Traditionally, a yard tractor cab is mounted on the frame using a four-point mounting system with mounts at two front points and two rear points. Generally, the front points are located at the front corners of the two main frame rails and the rear points are located towards the rear corners of the intersection of the cab and deck with the main frame.
The problem with the present four-point cab mounting system is the transmission of unwanted shocks and vibrations into the cab due to the absence of an axle-to-frame rear suspension. Since the traditional mounting method essentially fastens the cab (and/or deck) to the tractor main frame at four points, any shocks and vibrations subjected to the main frame (including any torsional frame twisting) are transmitted into the cab. This results in extreme discomfort to the operator. Further, increased costs are incurred to provide within the cab instrumentation and mechanisms capable of withstanding such shocks, vibrations and torsional twisting. Accordingly, there is a need for a cab mounting system which takes into account the unique characteristics of a yard tractor having a one-man cab configured on either the left or right hand side of the tractor and which is capable of reducing and preventing shocks and vibrations (including torsional twisting) from being transmitted to the cab. Further, there is needed a three-point mounting system having improved performance over the traditional four-point mounting system, which reduces the number of mounts required to mount the cab to the tractor frame. Additionally, there is a need for a rear cab mount capable of providing improved isolation of the cab from the frame to reduce torsional twisting of the cab and further reduce and prevent shocks and vibrations from being transmitted into the cab.